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The Tuning
Qualifications
Absolute Measurement Fundamentals
Changing the PTR
Changing the PTR
The peak tuning range (PTR) for the phase lock loop measurement is set by
the tune range entered for the VCO and the VCO's tuning constant. (If the
calibration technique is set to measure the VCO tuning constant, the
measured value will be used to determine the system's PTR.)
PTR= VCO Tuning Constant X Voltage Tuning Range
From the PTR, the phase noise software derives the capture and drift
tracking Ranges for the measurement. These ranges set the frequency
stability requirements for the sources being used.
The PTR also determines the phase lock loop (PLL) bandwidth for the
measurement. An important attribute of the PLL bandwidth is that it
suppresses the close-in noise which would otherwise prevent the system
from locking the loop.
Changing the PTR is accomplished by changing the tune range of VCO
value or the VCO tuning constant value or both. There are several ways this
can be done. However, when considering these or any other options for
changing the PTR, it is important to remember that the VCO source must
always meet the following tuning qualifications.
•
The tuning response of the VCO source must always remain monotonic.
•
The VCO source's output level must remain constant across its tuning
range.
6-14 Agilent Technologies E5500 Phase Noise Measurement System
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